Metadata Keys Parameter

To describe a dynamic metadata structure, you need to know what type to represent. This type reference is done by defining a @MetadataKeyId parameter in the operation that contains the ID of the type (for example, Account) that will be passed to the metadata resolver defined for that parameter.

This means, for example, that if your operation can save a generic record to a remote system, but you want to provide a better design-time experience by describing the supported types Account and Organization, then one of your operation parameters will be a type reference containing either the ID Account or the ID Organization. This parameter will be used to describe either the Account structure or the Organization structure for the record to be saved into the bucket, depending on what the end user decides to use.

Providing a List of Metadata Keys

The most common case when resolving dynamic metadata is to have a dynamic set of keys that identify each of the possible types to be resolved. At design time, the end user will configure the connector, select an operation, and choose one of those keys from the set that gets populated dynamically, and the selected key will become the MetadataKeyId for the metadata resolution.

Implementing the dynamic key’s resolution starts with a TypeKeysResolver:

public class RecordKeysResolver implements TypeKeysResolver {

  @Override
  public String getCategoryName() {
    return "Records";
  }

  @Override
  public Set<MetadataKey> getKeys(MetadataContext context) throws MetadataResolvingException, ConnectionException {
     // First we need to obtain the key IDs that will be used.
     // This is where you'd normally use `context.getConfig()`
     // or `context.getConnection()` to obtain the entity id's
     // from a remote service, for this demo the keys will be fixed
     List<String> keyIds = Arrays.asList("Author_id", "BookList_id", "Book_id");

     HashSet<MetadataKey> keys = new HashSet<>();
     for (String id: keyIds){
       // For each possible if, we create a new MetadataKey with that ID
       MetadataKeyBuilder builder = MetadataKeyBuilder.newKey(id);

       // Then, we add a DisplayName to that MetadataKey,
       // this will be the name shown in the UI
       builder.withDisplayName(StringUtils.removeEnd(id, "_id"));

       //finally, add the key to the Set of known MetadataKeys
       keys.add(builder.build());
     }

     return keys;
  }

}

Above, all the elements that are required to create a dynamic set of MetadataKeys. The method to implement is getKeys, which outputs all the keys available to the user.

The id element, like Author_id is used internally and must be unique for each structure that you want to represent across all the resolvers. The displayName is the name to show to the user for that key, so it is expected to be more user friendly and readable.

After the resolver is defined, you can use it as an operation or a source by adding the @MetadataScope annotation with its keysResolver value at the class definition level and annotating the parameter that is the key with @MetadataKeyId. All metadata resolvers must belong to the same category in an operation or a source.

@MetadataScope(keysResolver = RecordKeysResolver.class)
public class OperationWithMetadataKey {

    public void create(@MetadataKeyId String type,
                       @Config MyConfig config){
        //...
    }
}
@MetadataScope(keysResolver = RecordKeysResolver.class)
public class DocsMetadataSource extends Source<Map<String, Object>, Void> {

    @MetadataKeyId
    @Parameter
    public String type;

    //...
  }
The previous example is the only way to support metadata keys for sources. Do not set the resolver at the @MetadataKeyId annotation when defining sources.

Setting the @MetadataScope annotation at the operation class definition level indicates that all of its operations provide metadata and that they must all have a parameter annotated with @MetadataKeyId because they inherit the resolver from the scope.

You can also set a key resolver for a single operation:

public class MyOperations {

    public void operationWithMetadataKey(@MetadataKeyId(RecordKeysResolver.class) String type,
                       @Config MyConfig config){
        //...
    }

    public void plainOperation(@Config MyConfig config){
        //...
    }
}

In addition, if there is a @MetadataScope annotation at the operation class definition level, you can set a value for the @MetadataKeyId annotation in a parameter to override the resolver defined at the scope level for a single operation:

@MetadataScope(keysResolver = ClassLevelResolver.class)
public class MyOperations {

    public void operation(@MetadataKeyId String type, @Config MyConfig config){
        // This operation will use the ClassLevelResolver
    }

    public void operationWithAnotherResolver(@MetadataKeyId(OverridingResolver.class) String type,
                       @Config MyConfig config){
        // This operation will use the OverridingResolver
    }
}
The two previous examples (setting the resolver at the parameter level and overriding the inherited resolver from the scope) work only when defining operations. These features are not available for sources.

User-Defined MetadataKey

An user-defined MetadataKey is one that is provided freely by the end user and not defined by you as one of the possible elements of a List.

For example, this is a very common case in queries, where you use the whole query that the end user wants to execute as a MetadataKey.

To declare a user-defined MetadataKey, annotate a parameter with @MetadataKeyId without providing a TypesKeyResolver for the parameter annotation or for the @MetadataScope annotation if it is present at the class definition.

public class MyOperations {

  public void query(@MetadataKeyId String query){
      //...
  }
}

Optional MetadataKey Parameters

Available since version 1.3.

You can make MetadataKey parameters optional like other parameters, by adding the @Optional annotation:

public void query(@MetadataKeyId @Optional String query){
 //...
}

When an optional MetadataKey parameter is not assigned a value, metadata calls are made using null as the value of MetadataKey. This means that any MetadataResolver parameter associated with this MetadataKey parameter must be prepared to receive a null value.

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